Resin based dental restorative materials are becoming the material of choice by dentists and patients due to desirable aesthetic properties. Contemporary dental adhesives evolve rapidly because patients want their teeth to be restored functionally, esthetically, and invisibly. The conventional form of dental adhesives requires three steps with successive applications of 1) an acid etchant that is normally phosphoric acid, 2) an adhesion promoting agent or primer, and 3) a bonding resin or adhesive. Between the first and second steps, water rinsing and drying are generally required. Between the second and third steps, drying is required. After all these three steps, light-curing is generally required to polymerize and harden the adhesive. This procedure is complex and, hence, technique-sensitive.
Efforts have been directed toward developing new types of dental adhesives to simplify the above dental adhesive application procedure. A simplified two-step procedure combines the primer and adhesive steps into one step. One of the commercialized products is Optibond Solo Plus® (Kerr Corporation, Orange Calif.). After total etch with a phosphoric acid etchant, followed by water rinsing and drying, Optibond Solo Plus® is then applied to tooth structures. Superior bonding strength is generated after appropriate light curing. This “etch & rinse” technique is widely accepted to be an effective approach to achieve efficient and stable dental bonding. Another simplified two-step procedure combines the acid etchant and primer steps into one step. The combination of acid etchant and primer is generally called a self-etching primer, and one of the commercialized products is Optibond Solo Plus Self-Etch Primer® (Kerr). After application of Optibond Solo Plus Self-Etch Primer on a tooth structure, drying, but no water rinsing, is required. Superior bonding strength is generated after appropriate application of Optibond Solo Plus® adhesive followed by light curing. A two-component one-step dental adhesive, Adper Prompt L-Pop® (3M ESPE, St. Paul Minn.), combines all three steps, but requires mixing of two separated parts before applying the adhesive on a tooth substrate.
U.S. Pat. No. 6,387,979 describes a bonding composition with high initial bonding strength and good bond durability. The composition is a mixture of a polymerizable compound having an acid group, a water-soluble film-forming agent, water, and a curing agent, in which the calcium salt of the acid is insoluble in water, and the film-forming agent is a polymerizable compound miscible with a physiological saline solution. The composition does not require any pre-treatment such as acid-etching or priming treatment. U.S. Published Patent Application No. 2003/0187092 describes a one-bottle dental bonding composition that is applied onto a tooth without any pretreatment of the tooth surface. The composition contains a radical polymerizable monomer with an acidic group and the composition is substantially free of water. U.S. Published Patent Application No. 2004/0229973 describes a two-part and one-part self-etching adhesive containing dipentaerythritol pentaacrylate phosphoric acid ester and 4,4′-oxydiphenylether-1,1′,6,6′-tetracarboxylic acid-1,1′-(2-methacryloxy) dimethacrylate and/or 4-methacryloxyethyltrimellitic anhydride. U.S. Published Patent Application No. 2004/0254261 describes a one component dental composition in which a polymerizable compound having an acidic group is coexisted with a reducing agent such as a tertiary amine, water, and an alumina oxide powder.